mjhjmtu

I'm connected to local area network with access to the Internet through gateway. There is DNS server in local network which is capable of resolving hostnames of computers from local network.

I would like to configure systemd-resolved and systemd-networkd so that lookup requests for local hostnames would be directed (routed) exclusively to local DNS server and lookup requests for all other hostnames would be directed exclusively to another, remote DNS server.

In the configuration file for local network interface we have to either specify we want to obtain local DNS server address from DHCP server using DHCP= option:

[Network]
DHCP=yes

or specify its address explicitly using DNS= option:

[Network]
DNS=10.0.0.1

In addition we need to specify (in the same section) local domains using Domains= option

Domains=domainA.example domainB.example ~example

We specify local domains domainA.example domainB.example to get the following behavior (from systemd-resolved.service, systemd-resolved man page):

Lookups for a hostname ending in one of the per-interface domains are
exclusively routed to the matching interfaces.

This way hostX.domainA.example will be resolved exclusively by our local DNS server.

We specify with ~example that all domains ending in example are to be treated as route-only domains to get the following behavior (from description of this commit) :

DNS servers which have route-only domains should only be used for the
specified domains.

This way hostY.on.the.internet will be resolved exclusively by our global, remote DNS server.

Note

Ideally, when using DHCP protocol, local domain names should be obtained from DHCP server instead of being specified explicitly in configuration file of network interface above. See UseDomains= option. However there are still outstanding issues with this feature – see systemd-networkd DHCP search domains option issue.

We need to specify remote DNS server as our global, system-wide DNS server. We can do this in /etc/systemd/resolved.conf file:

[Resolve]
DNS=8.8.8.8 8.8.4.4 2001:4860:4860::8888 2001:4860:4860::8844

Don't forget to reload configuration and to restart services:

$ sudo systemctl daemon-reload
$ sudo systemctl restart systemd-networkd
$ sudo systemctl restart systemd-resolved

Caution!

Above guarantees apply only when names are being resolved by systemd-resolved – see man page for nss-resolve, libnss_resolve.so.2 and man page for systemd-resolved.service, systemd-resolved.

See also:

• 
  Description of routing lookup requests in systemd related man pages is unclear


• 
  How to troubleshoot DNS with systemd-resolved?

References:

• Man page for systemd-resolved.service, systemd-resolved


• Man page for resolved.conf, resolved.conf.d


• Man page for systemd-network